Gibbs Free Energy.

  • Thread starter luysion
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Main Question or Discussion Point

Hi, ive recently started studying chemistry and have being going over gibbs free energy.. I understand it is a driving force causing chemical and physical changes but during my course of reading I did have some queries stem to mind.

1) In relation to equilibrium why is it that a reaction occurs such that G is minimum ? I.e. i read that the reason neither the forward nor reverse reaction proceeds to completion during equilibrium is because Gibbs Free Energy is at a minimum. Is this due to no driving force being provided?

2) When gibbs free energy is positive it indicates the forward reaction (e.g. A --> B) is non-spontaneous why does it still occur? I read something about the reaction still proceeds but the pressure of the product does not read 10^5 P i.e. standard pressure?
im really confused on this bit can somone please simplify this

cheers for any help
 

Answers and Replies

  • #2
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Equilibrium can be viewed as compromise between two opposing tendency of the system:
1. to attain minimum energy (enthalpy)
2. of maximum molecular chaos (entropy)
remember this equation,
[tex]\Delta[/tex]G=[tex]\Delta[/tex]H-T[tex]\Delta[/tex]S
where [tex]\Delta[/tex]H is the enthalpy change, [tex]\Delta[/tex]S is the entropy change, and T is the temperature
A higher value of T[tex]\Delta[/tex]S signifies greater spontaneity. So as this parameter increases, [tex]\Delta[/tex]G becomes smaller and smaller. For Gibbs energy we hav, -[tex]\Delta[/tex]G[tex]\geq[/tex]0. At equilibrium, the two tendencies mentioned above are equal. So, [tex]\Delta[/tex]H=T[tex]\Delta[/tex]S; & [tex]\Delta[/tex]G=0.
To make a reaction with positive Gibbs energy occur, you just increase the temperature, that will increase the T[tex]\Delta[/tex]S factor in the equation.
 
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